Diffraction grating x-ray spectrometer wherein an electron beam is scanned across a fixed x-ray emitting element

ABSTRACT

A diffraction grating spectrometer having an X-ray tube in a fixed position, the ray-source of which is rapidly moved back and forth on a definite curve. Diffracted beams from the grating surface are focused on a slit of a fixed electronic counter and the intensities of the spectral distribution are observed or measured by a suitable means. The positions of the ray-source and the counter are the reverse of those in the previously known spectrometers.

United States Patent [72] lnventor Masao Sawada 525 lkejiri, Sayama-cho Minami Kawachigun, Osaka-Fu, Japan [2| Appl. No. 694,933

[22] Filed Jan. 2, 1968 [45] Patented May 4, 1971 [54] DIFFRACTION GRATING X-RAY SPECTROMETER WHEREIN AN ELECTRON BEAM IS SCANNED ACROSS A FIXED X-RAY EMITTING ELEMENT 6 Claims, 9 Drawing Figs.

[52] US. Cl 250/5l.5, 250/49.5 [51] Int. Cl G01n 23/22 [50] Field of Search 250/5 1.5, 49.5; 356/79 [56] References Cited UNITED STATES PATENTS 3,218,458 11/1965 Fumas 250/51.5 3,322,948 5/1967 Baak et al. 250/5 1 .5 3,384,756 5/1968 l-iasler et al. 250/5 1.5

Primary Exarriinen-Archie R. Borchelt Assistant Examiner-A. L. Birch Att0meyStephen H. Frishauf ABSTRACT: A diffraction grating spectrometer having an X- ray tube in a fixed position, the ray-source of which is rapidly moved back and forth on a definite curve. Diffracted beams from the grating surface are focused on a slit of a fixed electronic counter and the intensities of the spectral distribution are observed or measured by a suitable means. The positions of the ray-source and the counter are the reverse of those in the previously known spectrometers.

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I GXX DIF FRACTION GRATING X-RAY SPECTROMETER WHEREIN AN ELECTRON BEAM IS SCANNED ACROSS A FIXED X-RAY EMITTING ELEMENT BACKGROUND OF THE INVENTION This invention relates to a grating spectrometer used for spectral distribution of any kind of rays such as a-rays, B-rays, 'y-rays, X-rays, radio waves, light rays, sound waves etc.

The usual spectrometer having a plane or concave grating has been widely utilized for spectroanalysis or other purposes, and consists of a fixed radiation source and a photographic or movable counter. However, the construction and the operation of such spectrometer is complicated. The development of sensitive. electronic counters with delicate and complex cooling systems makes movements of the undesirable.

It would be desirable to have a spectrometer with a simple electronic counter at a fixed position.

An object of the present invention is to provide a spectrometer which overcomes the above-mentioned troubles.

Another object of the present invention is to achieve accurate and rapid measurements of faint X-ray lines such as X-ray satellites.

SUMMARY OF THE INVENTION designed microfocus X-ray tube that can scan the cathode-ray beams by electron beam deflectors as in the well known electron optics used in television and curve followers.

BRIEF EXPLANATION OF THE DRAWINGS FIG. 1 is an illustrative diagram of the principles of known concave grating spectroscopy;

FIG. 2 is an illustrative diagram of loci of point wave sources and their images for concave grating spectroscopy according to the present invention;

FIG. 3 is an illustrative diagram of one embodiment of the present invention utilizing Rowland circle;

FIG. 4 is an illustrative diagram of another embodiment of the present invention using plane grating;

FIG. 5 is a schematic diagram of the plane grating spectrometer according to FIG. 4;

FIG. 6 is an illustrative diagram of another embodiment of the present invention using concave grating;

FIG. 7 is an illustrative diagram of the scanning direction of a wave source in the present invention;

FIG. 8is a schematic diagram of the travelling mechanism of the X-ray tube of the novel spectrometer according to FIGS. 6 and 7; and

FIG. 9 is a partial schematic diagram of a travelling mechanism of the counter correlated to that of FIG. 8.

DETAILED DESCRIPTION The relation between wave sources and their images will be mentioned briefly. The case of plane grating can be treated as a special case of concave grating, and so the concave grating will be treated first.

In .F IG. 1, there is shown a cross-sectional part of the spherical surface of a concave grating defined by a circular arc CC. G and G are the traces of ruled grooves thereon, that is, elements of the grating. The divergent X-rays, hereafter the case ofrX-rays' is adopted as one of general rays radiating from a point sources .8 (r, 9.), are assumed to be focused at a point F (p, D). Considering the path difference between the lines SG,F and SG F, the following equation is well known,

where d, k, n, 9 and P are the grating constant, wavelength, its spectral order, angle of incidence and angle of reflection respectively.

The direction of the diffracted beam can be determined by Eq. l but yet there remains the problem of determining the magnitude of the vector of the diffracted beam. This is determined as follows. Two circles are described whose centers are at S and F with radii SG,=r and FG =p and their intersection with SG, and FG, are designated H and I respectively. Let the central angle G,OG be m. This angle and an arcfiigth G 6 are very small compared to 9 1 r and p. G H and 6,1 are to be regarded as perpendiculars dropped to SG and FG respectively. We then have following relations in the triangles AG HG AND AG lG 4 Next, in the triangles ASG G and AFG,G equating the sum of the two inner angles to that of the external angle of the third one, we have respectively,

d =e'w (6) where angles 9 and I are not independent of each other, but we have the following connection by differentiation of Eq. (1).

Substituting in the last formula the value of d9 and d I of Eqs. (5 and (6), we have the grating formula sin 0 sin 0 sin sin qS) R) (P R 0 (8) When polychromatic and divergent X-rays emerge from a point S (r, 9), the loci of their foci (p, 1 of diffracted beams are determined by using a separation constant D that is a parameter, therefore we have sin 0 sin l p R D and from Eqs. (8) and (9), we have for incident beams,

sin 0 sirg9 1 7 R D (10) Now from Eqs. (9) and (10), We obtain R sin 42 T R sin D 1) and R sin 6 R sin 6 Eqs. l 1) and 12) are mutually conjugate.

The pand r-curves are called source and image curves, respectively, and vice versa. When one of them takes a negative value, it is the-virtual image and is behind the grating at some distance on the same line. In such case, a divergent must be used.

When we choose the parameter D as the above two equations reduce to a single circle r=R sin 6, p=R sin I both of them being the well-known Rowland circle as shown in FIG. 3. In this special case, the two curves (r, 6) and (p, Q) are self-conjugate.

Next in the two equations (9) and (10), let us choose any parameter D, and we can find their loci by a numerical calculation or a graphical method. When one curve becomes an oval (a closed curve), then its conjugate becomes an open V-, U-, W- or (Mike curve having two asymptotes and two inflection points as shownin FIG. 2.

The shortest distance from the midpoint of the grating to a point of (p, 9) curve, which is a very important item in the practical grating spectrometer, lies in the following direction,

sin where D 2R,' (13) otherwise, 1 is imaginary, because sin 1 1.

And further we can see that it lies on a circumference of a circle whose center is at C, and having a radius of the grating R, as shown in FIG. 2,

p=2R sin 1 14) Secondly, we can find after some lengthy calculations, that the coordinates of their inflection points satisfy the following equation,

and the inflection points lie in the following direction,

sin I =(D+ 1/I) +l8R )/3R (16) Moreover, the very special point which has a shortest distance and an inflection point can be obtained by equating sin (I of Eqs. (13) and I5), and the parameter D becomes This special case is illustrated by a diagram shown in FIG. 2, and the circle of Eq. (14) is called the Sawada circle hereafter.

The design of a novel grating spectrometer in the present invention is based on the principle of reversibility of optical paths. Namely the positions of a wave source and its focus can be exchanged mutually. If a ray-source is located at a point F(p, 1 in FIG. 1, the divergent rays from F difiract on the grating G G to focus at a fixed point S(r, 6), and Eqs. (II) and 12) come into existence exactly, where D is a parameter Generally, the novel grating spectrometer in the present invention consists of an electronic scanning ray-source which is positioned at a point (p, 1 and a fixed electronic counter which is fixed at a point (r, 6). The relations which apply are given in the general formulas p: R sin sin and R sin 0 v sin 0+% where,

R Radius of the concave grating.

p Distance from the scanning ray-source to the midcenter i of the gratmg.

d Incident angle of divergent rays from the ray-source upon the grating.

r Distance from the midcenter of the grating to the slit of counter.

9 Angle of diffracted rays from the grating to the slit of counter. V

D a parameter (0S; Dg

These formulas are similar to Eqs. of I l and 12).

There will now be described particularly three embodiments of spectrographic apparatus.

I. The case of utilizing Rowland mounting.

In this case, asmall range of wavelengths can be treated. In FIG. 3, the X-ray point source F, having a few square microns in area, of white radiation lies on the Rowland circle E, and moves back and forth by a small amount (such as a few millimeters) on a fixed straight line which is a tangent to the Rowland circle E at F ..Then all spectral images obtained by the diffraction on the grating G focus on the fixed slit S of the counter A, which lies also on the same Rowland circle E, that is 7=R sin9 and p=Rsin I as mentioned before.

II. The case of plane grating.

In the case of a plane grating, letting R= in Eqs. of abovementioned general formulas, the following reduced equations are obtained.

p= -D sin I and r=D sin G When the parameter D is eliminated, we have R sin rsin 6 The mutual curve becomes an oval of the same in size and shape but symmetrical with respect to the tangent which touches the midpoint of the grating. (Not shown in the FIGS.) This oval is flat on the top. Thus, the divergent slit must be used.

When we choose I =60 A, the tangent to an oval at this point (that is, the scanning direction) becomes normal to the surface of the grating G as shown in FIG. 4, and maximum dispersion just lies in the direction l =54l 2h FIG. 5 is a schematic diagram of this plane grating spectrometer as a whole. Electron beams of an X-ray tube derived from a cathode filament K pass through a deflecting electrode D, and collide against the anticathode surface F to produce X- rays. The divergent X-rays are diffracted by the plane grating G to focus at the divergent slit S of a fixed electronic counter H. In the compartment A, there is a high voltage apparatus for generating the X-rays, and an electric source for the deflecting electrode etc. The counter A is connected to a multiple-channel-sealer X which provides, with a Brawn tube B, for direct observation of the spectral distribution. The sealer X is used not only for the direct observation, but for recording wavelengths and intensities of the spectrum and integrating the intensities thereof as a function of time.

T is a vacuum tank which contains cathode filament K, deflecting electrode D, anticathode F, grating G and counter A therein.

III. The case of Sawada mounting.

There is illustrated a Sawada mounting in FIG. 6, in which T is a vacuum tank with a radius of a little larger than that of the concave grating G. Within it, a circular track having the same radius as the concave grating G is provided. A track carrying an X-ray tube can be displaced along the circumference of the track, and can be set to the angular position I according to the wavelength to be examined by Eq. (1), and also restricted by the angular position 6 of the prefixed counter C.

The electronic scanning direction of the point-focuscathode-ray beam is determined as follows:

In FIG. 2, the curve l-l' is the loci of (p, 1 curve determined by Eq. (11), but if the minimum distance from G is chosen, this point on the curve must satisfy Eq. (13 Then the curve 1-1 should be rewritten as Eq. (14). The minimum points, as a function of 1 namely as a function of wavelengths, lie on the circle with a radius R, that is, the Sawada circle.

Then the position (r, 9) of the slit S of the fixed counter C is R iri b 1 sm 0 S111 2 is) from Eqs. (12) and (13). If a tangent F0 is drawn to the curve l-l' at F in FIG. 2 and as shown in FIG. 7, then its inclination dy and the inclination of the incident beam is tan 1 Hence, evidently FG and F0 intersect at right angles to each other. It is very interesting that, on the Sawada circle, at any point F, the tangent thereat to the (p, 1 u rve passing through F is at a right angle to the radius vector GF. Thus the direction of the scanning is always on the straight line that passes through the point 0, diametrically opposite point G as shown in FIG. 7.

In the case of measuring of a very wide spectral region, the fixed positions of the counter are allowed to be as in the cases of embodiments I and II. lnvthe case of embodiment III, however, the counter must be moved as well as the X-ray tube along the fixed beam (9 constant) when the measurement of extremely extended spectral regions is required. The X-ray tube must be moved from the fixed position to another, as shown in F IG. 8, from the solid line to a dotted line successively. As the tube-holding beam OF turns, the X-ray tube slides on this beam, but its relative motion to the beam is only translational displacement without rotation of the X'ray tube. The period of a rotation of the X-ray tube about its own axis is just one-half of the period of the revolution of the X-ray tube around the center of the Sawada circle.

ln synchronism, the counter can be moved along the fixed .beam (6 constant) by the mechanism as shown in FIG. 9. in this FlG., a solid beam X,X can rotate about the midpoint G of the grating, and the counter can slide freely along this beam. Another beam X X' is set parallel to the arm X X and these two parallel beams are made to be separated from each other by the distance\ R sinG. Two concentric circular discs with radii of unit length (G-disc) disc) and of one-half unit length I -disc) disc) are made to slide freely along the beam X X' The discs can be rotated independently, but they are always concentric. These two discs are provided for making the distance (sin O-l-Bsin 1 between two vertical sides to P P S 8 and P P P' of two L-shaped beams and S 88 and making these two L-shaped beams to slide on the arm X X according to the variation of the X-ray tube s position.

Namely, a pin A fixed to G-disc, whose distance from the axis of the G-disc is the unit length (for example, 1cm. passes through the guiding beam P P If we make an angle HOA as 6, the distance F 0,. becomes just equal to sine. Similarly there is another pin B attached to the I -disc, and it can freely slide on the beam SS If we make an angle l-lB as 1 the distance 6 5,-, becomes equal to vt sinG. Therefore, P 8, is equal to (sin9+%sin l Next, the right angular apex SX of another L-shaped beam P S is caused to slide on the beam X X' and simultaneously make two beams S 6 and S P of the beam to pass through PX and G respectively. In the right angular triangle AGSX PX we have PISXS G=SS ,JbXRsin G If we put the slit of the counter at S, putting fir, Eq. (18) is exactly satisfied.

The counter may be placed on the platform shown with S5,, of the right angular beam S SSX' Thus the X-ray tube and the counter can be moved synchronously, by mechanical or electrical coupling methods and there can be obtained the wide range of wavelengths as time resolved spectra successively and rapidly.

By using this spectrometer set at the spectral region of faint X-rays, it is possible to carry out the measurement in a few minutes and in a fixed position whereas the conventional photographic method requires several dozens or hundreds of hours for such measurement.

The mechanisms of Rowland mounting are simple, but the astigmatic aberrations are rather large. 0n the contrary, Sawada mounting provides better performance with regard to astigmatic aberrations.

The ray-source has been mainly concerned with X-rays, but it is also applicable to all ranges of electromagnetic and corpuscular radiations and sounds including liquid surface waves.

lclaim:

l. A diffraction grating spectrometer comprising:

an X-ray tube including an X-ray emitting element mounted at a fixed position along a source focal curve represented by p=R sin%( sin@/ R/D),

a means for generating an electron beam, and means for scanning said electron beam across said x-ray emitting element;

a fixed grating mounted proximate to an image-focal curve represented by r=R'sin 9/ (sin 9+R/D) for receiving X- rays from said source; and

an electronic counter having a slit on which the diffracted rays of different wavelengths, determined by the grating equation expressed by nk=d (cost 9cos l are focused by said grating, said slit being mounted at fixed position on the image-focal curve, where:

A the middle wavelength to be examined;

n the spectral order;

d the grating constant;

R the radius of the concave grating;

p the distance from the X-ray source to the midpoint of the grating;

CI the angle of incidence;

r= the distance from the slit of counter to the midpoint of grating;

9 the fixed angle of diffraction; and

D a parameter connecting a pair of the sourceand image-curves.

2. A spectrometer according to claim 1 wherein said scanning means electronically scans said electron beam across said X-ray emitting element.

3. A diffraction grating spectrometer comprising:

an X-ray tube including an X-ray emitting element mounted at a fixed position along the source-focal circle represented by p=R sin I means for generating an electron beam, and means for scanning said electron beam across said X-ray emitting element, the scanning direction being tangential to said source-focal circle;

a fixed concave grating mounted proximate to the imagefocal circle represented by r=R sine for receiving X-rays from said source; and

an electronic counter having a slit on which the diffracted beams of different wavelengths, determined by the grating equation expressed by n \=d(cos9cos@), are

focused by said grating, said slit being mounted at a fixed position on the image focal circle, where:

)t the middle wavelength to be examined;

n the spectral order;

d the grating constant;

R the radius of concave grating;

p the distance from the X-ray source to the midpoint of the grating;

1 the angle of incidence;

r the distance from the slit of the counter to the midpoint of the grating; and

6 the fixed angle of diffraction.

4. A spectrometer according to claim 3 wherein said scanning means electronically scans said electron beam across said X-ray emitting element.

5. A diffraction grating spectrometer comprising:

an X-ray tube including an X-ray emitting element mounted at a fixed position along the circle represented by p=2R. sind means for generating an electron beam, and means for scanning said electron beam across said X-ray emitting element;

a fixed concave grating mounted proximate to an imagefocal circle represented by r=Rsin (sin9+ /BsinI for receiving X-rays from said; and

the scanning direction being perpendicular to a straight line between the midpoint of the grating surface and the center of said X-ray emitting element;

an electronic counter having a slit on which the diffracted beams of different wavelengths, determined by the grating equation expressed by n)t=d(cos6cos b), are focused by said grating, said slit being mounted at a fixed position on the image-focal curve; where:

A the middle wavelength to be examined;

n the spectral order;

d= the grating constant;

R the radius of the concave grating;

p the distance from the X-ray source to the midpoint of the grating;

I =the angle of incidence;

r the distance from the slit of the counter to the mid point of the grating; and

9 the fixed angle of diffraction.

6. A spectrometer according to claim 5 wherein said scanning means electronically scans said electron beam across said X-ray emitting element. 1

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 577 1 59 Dated May 4 1971 Masao Sawada Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet insert [32] Priority Aug. 29, 1967; Sept. 16, 1967 and Sept 30 1967 [33] Japan [31] 42/55437; 42/ 59551; and 42/63202 Signed and sealed this 17th day of August 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents FORM po'mso H0459) USCOMM-DC 60376-1 69 US GCIVERNMFNT PRINYINQ CIFFIC I959 U366JIH 

2. A spectrometer according to claim 1 wherein said scanning means electronically scans said electron beam across said X-ray emitting element.
 3. A diffraction grating spectrometer comprising: an X-ray tube including an X-ray emitting element mounted at a fixed position along the source-focal circle represented by Rho R sin phi , means for generating an electron beam, and means for scanning said electron beam across said X-ray emitting element, the scanning direction being tangential to said source-focal circle; a fixed concave grating mounted proximate to the image-focal circle represented by r R sin Theta for receiving X-rays from said source; and an electronic counter having a slit on which the diffracted beams of different wavelengths, determined by the grating equation expressed by n lambda d(cos Theta -cos phi ), are focused by said grating, said slit being mounted at a fixed position on the image focal circle, where: lambda the middle wavelength to be examined; n the spectral order; d the grating constant; R the radius of concave grating; Rho the distance from the X-ray source to the midpoint of the grating; phi the angle of incidence; r the distance from the slit of the counter to the midpoint of the grating; and Theta the fixed angle of diffraction.
 4. A spectrometer according to claim 3 wherein said scanning means electronically scans said electron beam across said X-ray emitting element.
 5. A diffraction grating spectrometer comprising: an X-ray tube including an X-ray emitting element mounted at a fixed position along the circle represented by Rho 2R sin phi , means for generating an electron beam, and means for scanning said electron beam across said X-ray emitting element; a fixed concave grating mounted proximate to an image-focal circle represented by r Rsin2 Theta / (sin Theta + 1/2 sin phi ) for receiving X-rays from said; and the scanning direction being perpendicular to a straight line between the midpoint of the grating surface and the center of said X-ray emitting element; an electronic counter having a slit on which the diffracted beams of different wavelengths, determined by the grating equation expressed by n lambda d(cos Theta -cos phi ), are focused by said grating, said slit being mounted at a fixed position on the image-focal curve; where: lambda the middle wavelength to be examined; n the spectral order; d the grating constant; R the radius of the concave grating; Rho the distance from the X-ray source to the midpoint of the grating; phi the angle of incidence; r the distance from the slit of the counter to the midpoint of the grating; and Theta the fixed angle of diffraction.
 6. A spectrometer according to claim 5 wherein said scanning means electronically scans said electron beam across said X-ray emitting element. 